A communication service that connects between information systems of users, such as of an enterprise, located at sites separated by distances, such as between cities, is called a wide area network service. Conventionally, comparatively expensive communication services connecting between the information system bases of the user, such as a private line and an ATM network, are used for the wide area network services. In recent year, IT of enterprise businesses have been enormously developed, and various pieces of information have been communicated between bases of an enterprise after being converted into electronic forms. In order to respond to such demands, the wide area Ethernet (registered trademark) that is easy to be connected to a user's information system at a lower cost and IP and Ethernet based wide area network services, such as an IP-VPN, have become increasingly used.
The IP and Ethernet based wide area network provides connection ease with a user's information system by utilizing a router device (hereinafter abbreviated as a router) by the use of IP that is a network standard protocol being used in the user's information system and a Ethernet technology. Moreover, interfaces that connect the routers use a transmission technology of a 10-Gbps wide band, and the IP and Ethernet based wide area network is made to be able to provide low cost services by a plurality of users sharing this wide band interface.
The IP and Ethernet based wide area network is constructed with core networks including router groups that form a foundation of the wide area network and edge routers each being a router for connecting the core network and a user's base. The communication packet used for communication between users' information system bases is encapsulated by the edge router, and a core network header used for communication within the core network is added to the communication packet. Since the router in the core network transfers the communication packet referring to the core network header, it can perform communication that uses the wide area network without altering the original user's communication packet.
In order for a plurality of users to share the wide area network, a user identification label for identifying a user is attached in the core network header. The router and edge router in the core network constitute a virtual private network for each user with the user identification label in the core network header, and are maintaining securability so that the communication packets between users may not be mixed mutually.
On the other hand, for sophistication of the network services, a service that provides a function of processing the user's communication packet has become increasingly used in addition to the above-mentioned wide area network service. There are various functions as a function of processing the communication packet, which include, for example, a monitoring function of the communication packet, a cache function of the communication packet, etc. As the packet processing unit for providing a processing of the communication packet, there are considered a computer device equipped with a general purpose CPU typified by Intel architecture (“Intel” is a registered trademark), a packet processing unit equipped with a network processor specialized in the packet processing, a packet processing unit equipped with a specific packet processing IC, etc. These packet processing units are selected in terms of high speed processing capability and programmability that are required as a communication packet processing function provided as a service.    [Patent document 1] U.S. Pat. No. 7,307,990    [Patent document 2] U.S. Pat. No. 7,185,106